Surface and root inputs produce different carbon to phosphorus ratios in soil

Authors: Wuest, Stewart; Reardon, Catherine - Kate

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2016
Publication Date: 4/22/2016
Publication URL: http://handle.nal.usda.gov/10113/5927836
Citation: Wuest, S.B., Reardon, C.L. 2016. Surface and root inputs produce different carbon to phosphorus ratios in soil. Soil Science Society of America Journal. 80:463-471.

Interpretive Summary: Formation of soil organic matter from crop roots and residues is important to maintaining soil productivity. In order to better understand what can be done to increase soil organic matter, we measured the effect of different natural substances applied to soil for a 5-yr period. Seven years after the applications ended, effects of wood, alfalfa, manure, and municipal biosolid were greater than wheat residue, sugar, mustard residue, cotton, wheat compost, or the un-amended check. Soil carbon increases ranged from 3 to 49% of carbon applied and had changed little in the last 28 months. The effect of amendments on soil carbon was highly correlated to phosphorus content of the amendments. Plots sown to continuous winter wheat during the period of amendment had 10% more SOC than plots that had been fallow, an effect over twice as large as most amendments. Also, the carbon to phosphorus and carbon to sulfur ratios were significantly greater in wheat-cropped soil. The increase in soil carbon caused by wheat plants and a perennial grass plot suggests that the contribution of roots was more important than aboveground crop residues. In summary, a five-year amendment period with aboveground biosolid, manure, and wood, or the roots of five years of wheat cropping or perennial grass, produced substantial soil carbon increases whereas much smaller increases were achieved by application of crop residues or sugar. The relative differences in soil carbon remained stable for seven years after the treatments ended and were correlated to phosphorus content of the amendments.

Technical Abstract: Formation of soil organic carbon (SOC) is influenced by inputs. We applied organic amendments for five consecutive years at 250 g C m 2 yr 1. Seven years after the applications ended, effects of biosolid and manure on SOC were greater than alfalfa, wood, wheat residue, sucrose, brassica residue, cotton, wheat compost, or the un-amended check. Soil C increases ranged from 3 to 49% of C applied and had changed little in the previous 28 months. Plots sown to continuous winter wheat during the period of amendment had 10% more SOC than plots that had been fallow, an effect over twice as large as most amendments. This suggests that the contribution of roots to SOC was more important than aboveground crop residues. The effect of amendments on SOC was highly correlated to their initial P content. In addition, for a similar available soil P and soil S content, SOC was significantly greater where wheat or perennial grass was grown. Wood caused an increase in C:N ratio that persisted over 3.5 years, but almost disappeared by the seventh year. This study indicated that continuous cropping or addition of animal waste or municipal biosolid had the greatest impact on the formation of SOC and this positive effect remained stable for many years after the end of the continuous treatment application.